Kinematic holding system for a placement head of a placement apparatus

ABSTRACT

A kinematic holding system for a placement head of a placement apparatus comprises a placement head alignment device which comprises at least one length-variable holding member arranged at a distance from a joint between a placement head support and the placement head. This holding member determines the pivoting position of the placement head relative to the placement head support. The length of the holding member is changeable during the placement operation depending on a deformation of the placement head guide device caused by the pressing force of the placement head against the substrate in such a way that an axis error (tilt) of the placement head caused by the deformation of the placement head guide device is compensated.

PRIORITY CLAIM

Applicant hereby claims foreign priority under 35 U.S.C §119 from GermanApplication No. 102012014558.6 filed Jul. 24, 2012, the disclosure ofwhich is herein incorporated by reference.

FIELD OF THE INVENTION

The invention concerns a kinematic holding system for a placement headof a placement apparatus for mounting electronic or optical componentson substrates, particularly in the semiconductor industry.

BACKGROUND OF THE INVENTION

Placement apparatuses in the semiconductor industry need to operate withhigh precision and high throughput. One example for such placementapparatuses are die-bonders or pick-and-place machines with whichcomponents in form of semiconductor chips are placed and bonded onsubstrates such as lead frames. The components are received in a pickingstation by the placement head, especially by means of suction, moved viaan XYZ handling system of the placement apparatus to the point ofplacement above the substrate, and placed thereafter at a preciselydefined position on the substrate. The placement head is fixed to aplacement head support and coupled to the XYZ handling system via saidsupport. The Z direction usually corresponds to the vertical direction,whereas the XY plane forms the horizontal plane.

In addition to a highly precise placement of the components in the XYplane, it is further very important that the components are also placedin a plane-parallel manner on the substrate. Tilted placement of thecomponents can lead to undesirable properties such as reduced holdingforce, worse or missing electric contacts, uneven heat transfer betweenthe components and the substrate, or damage to the components.

During the placement process it is a considerable problem that when thecomponent is pressed onto the substrate reaction forces will be producedas a result of the generated pressing forces which are far frominconsiderable, which reaction forces can lead to a deformation of theplacement head guide device, i.e. the placement head support and/or theXYZ handling system. In a placement head which is rigidly connected tothe placement head support this deformation leads to a tilting of theplacement head and therefore to an axis error (“tilt”) which produces arespective inclined position of the component relative to the surface ofthe substrate and furthermore to an undesirable offset of the componentin the XY plane.

Such a deformation which occurs in the state of the art is schematicallyshown in FIG. 2. The axial or inclination error which is caused by thedeformation-induced tilting of the placement head 2 together with theplacement head support 1, starting from the unloaded position as shownin FIG. 1, is designated there with “tilt”. The additionally occurringlateral offset at the bottom end of the placement head 2 on which thenot shown component is held is designated with “a”. “F” indicates thereaction force acting on the placement head 2, which reaction force isproduced by the pressing force when the placement head 2 is pressedperpendicularly onto the substrate 3.

It is known for avoiding this undesirable axis error to make theplacement head support as stiffly as possible. Despite optimizedtechnology in lightweight construction, this inevitably also leads to arelatively large mass. As a result of the massive configuration, thethroughput of the placement apparatus will decrease considerably atgiven drive power. Furthermore, it can never be prevented entirely evenin the case of a highly massive arrangement of the placement headsupport that the placement head will always yield slightly at its tipwhich accommodates the components when it is pressed onto the substrate.

It is a further known approach to arrange the placement head support ina symmetrical way. In the case of this symmetrical arrangement, theplacement head will be supported evenly on both sides. Although thisprevents the tilting of the placement head which is caused by thepressing force, the arrangement of the placement apparatus, and inparticular the placement head support and the placement head, will belimited very strongly with respect to its design. This leads todisadvantages in machine design like reduced accessibility, as well ascomplex or a high number of components.

A placement head holding system is known from WO 2008/052594 A1. Theplacement head is tiltably fixed there to the tool holder by means of asliding joint which comprises an air bearing. The compensation of theinclined position of the placement head occurs in such a way that theplacement head is placed without the component with released air bearingon the substrate, wherein the placement head will automatically alignrelative to the placement head support in such a way that the bottomface of the placement head is parallel to the substrate surface. The airbearing is locked thereafter and the placement head lifted from thesubstrate. The adjusted tilting angle of the placement head relative tothe placement head support is maintained in this process and is used forthe subsequent placement processes. Furthermore, an adjusting apparatusis indicated in a merely symbolic manner, by means of which apositioning of the placement head is possible with activated airbearings when a specific tilting position is to be set without pressingagainst substrate. WO 2008/052594 A1 therefore merely concerns apresetting of the placement head which is performed prior to the actualplacement process. A continuous compensation of the axis error of theplacement head during the placement process is not possible with thisknown holding system.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of providing a holdingsystem for a placement head which enables a highly precise,plane-parallel placement of the components on the substrate with highplacement force and high throughput, even with asymmetric placement headsupports, without having to arrange the placement head guide device inan especially stiff manner.

In a holding system in accordance with the invention, the placement headalignment device comprises at least one length-variable holding memberwhich is arranged at a distance from a joint between the placement headsupport and the placement head, and which determines the pivotingposition of the placement head relative to the placement head supportand whose length is variable during the placement operation depending ona deformation of the placement head guide device caused by the pressingforce of the placement head on the substrate in such a way that an axiserror of the placement head which is caused by the deformation of theplacement head guide device is compensated.

It is therefore characteristic for the holding system in accordance withthe invention according to claim 1 that a length-variable holding memberis provided, wherein the holding member, as a result of its change inlength, produces a pivoting movement of the placement head relative tothe placement head support about the joint via which the placement headis supported on the placement head support. The length-variable holdingmember may concern a passive element in the form of a spring, or anactive element in the form of a travel-controlled or force-controlledactuator.

This allows adjusting the inclination, i.e. the tilting position of theplacement head, in a continuous way during the placement operation toany deformations of the placement head guide device, i.e. the XYZhandling system and/or the placement head support. A kinematic holdingdevice for a placement head is therefore created which enablesminimization of the placement error in combination with simultaneousavoidance of high stiffness. The invention therefore allows theachievement of a distinct reduction in the mass, by means of which theplacement throughput will be increased substantially in combination withthe same drive power.

In accordance with an advantageous embodiment, the length-variableholding member has a longitudinal axis which is arranged parallel to thelongitudinal axis of the placement head, wherein the holding member andthe joint are especially arranged on opposite sides of the longitudinalaxis of the placement head. As a result, the reaction force which isproduced during the pressing of the component against the substrate canbe transferred in a simple manner both via the joint and also via thelength-variable holding member from the placement head onto theplacement head support. The length of the holding member will then beadjusted according to the deformation-induced displacement of the jointin a passive manner, especially by means of a spring, or in an activemanner by actuators, so that the desired axial position of the placementhead is also maintained during any deformation of the placement headguide device.

It is principally possible that the longitudinal axis of thelength-variable holding member is arranged at a random angle of between0° and 90°, especially also transversely, i.e. at 90°, to thelongitudinal axis of the placement head.

In accordance with an advantageous embodiment, the placement headalignment device comprises a plurality of joint rods which are connectedvia joints both to the placement head and also to the placement headsupport, and hold the placement head in a predetermined variableposition relative to the placement head support, wherein the relativeposition of the joint rods is variable by means of the length-variableholding member in such a way that the deformation-induced axis error ofthe placement head is compensated.

According to an advantageous embodiment, the length-variable holdingmember consists of a passive element in the form of a spring which isarranged in such a way between the placement head support and theplacement head that the pressing force is transferred from the placementhead support to the placement head by the joint on the one hand and viathe spring on the other hand, wherein the reaction force produced by thepressing force produces a change in length of the spring. This change inlength is adjusted to a deformation-induced displacement of the joint insuch a way that the angular position of the placement head relative tothe substrate is maintained during the pressing process even in the caseof a deformation of the placement head guide device.

Alternatively, the length-variable holding member can also consist of atravel-controlled or force-controlled actuator, especially an electricdirect drive, a voice coil or a piezo drive. Stepper motors, DC motorsor servomotors can especially be considered as electric direct drives.

In the event of insufficient force effect, a transmission can beprovided in the form of a lever arrangement or in the form of a gearwith which the actuator acts on the axial position of the placementhead. A spindle drive can especially be considered as the gear.

The placement head alignment device preferably comprises a motionblocking device for blocking relative movements of the placement headrelative to the placement head support. Uncontrolled free movements ofthe placement head relative to the placement head support can beprevented in this manner when the placement head is rapidly displaced,accelerated and braked. Such a blockage of movement will appropriatelybe formed in such a way that the actuators are built as lockableactuators. It is also possible as an alternative to provide a lockingdevice in addition to the actuators between the placement head and theplacement head support, which locking device is separated from theactuators.

Preferably, the placement head is suspended in its upper or bottom endregion in pendulum fashion on the placement head support and supportedin the Z direction by means of a joint which has at least one rotarydegree of freedom. Furthermore, at least one length-variable holdingmember for adjusting the inclination of the placement head relative tothe placement head support is provided in this case beneath or above thejoint. The placement head is therefore arranged in this case as aone-dimensional or multi-dimensional pendulum, especially atwo-dimensional pendulum. The joint can be built especially as asingle-axis joint, ball-and-socket joint or a universal joint (alsoknown as Cardan joint).

Preferably, a plurality of length-variable holding members is provided,which are arranged in such a way that they act on the placement headfrom different directions, so that the placement head is pivotable in amulti-dimensional way in space. This allows a purposeful adjustment ofthe inclination of the placement head in space in order to compensatedeformation-induced axis errors of the placement head.

The initially mentioned object is further achieved by a kinematicholding system according to claim 15. In accordance with thisembodiment, the placement head alignment device comprises at least onesolid joint element with at least one first solid joint arm which isrigidly connected to the placement head support, and at least one secondsolid joint arm which is rigidly connected to the placement head andelastically connected to the first solid joint arm by means of a solidjoint. The second solid joint arm is deformable in relation to the firstsolid joint arm depending on a deformation of the placement head supportcaused by the pressing force of the placement head on the substrate insuch a way that an axis error of the placement head caused by thedeformation of the placement head support is compensated.

Preferably, the rotational axis of the joint is arranged relative to adeformation rotational axis about which the deformation of the placementhead guide device occurs in reaction to the pressing force in such a waythat straight lines through the rotational axis of the joint and thedeformation rotational axis in the unloaded and loaded state of theplacement head are disposed in an angular range of between −45° and +45°with respect to a horizontal plane in which the deformation rotationalaxis 25 is disposed. This not only allows to compensate the axis error,but also to minimize the lateral offset by which the component isdisplaced by the deformation of the placement head guide device in theXY plane. This minimization of the lateral offset will be especiallyeffective when according to an advantageous embodiment the rotationalaxis of the joint lies beneath the deformation rotational axis in theunloaded state of the placement head, and above the deformationrotational axis under full placement force. It is especiallyadvantageous if at half the placement force the rotational axis of theplacement head is situated at the same level as the rotational axis ofthe placement head guide device, because in this case the lateral offsetis especially low in the end position of the component, or it can beavoided completely.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent invention and, together with the detailed description, serve toexplain the principles and implementations of the invention. The figuresare drawn schematically and not to scale. In the drawings:

FIG. 1 shows a schematic illustration of a placement head in theunloaded position which is rigidly connected to the placement headsupport, according to the state of the art;

FIG. 2 shows an illustration according to FIG. 1 for illustrating adeformation-induced axis error during the pressing of the placement headagainst a substrate;

FIG. 3 shows a schematic illustration of a holding system in accordancewith the invention, whose principal configuration approximatelycorresponds to the one of FIGS. 16 to 19, in the unloaded state,including the indication of the relative position of the rotationalaxes;

FIG. 4 shows the holding system of FIG. 3 in the unloaded and loadedstate for illustrating a minimal lateral offset;

FIG. 5 shows a side view of a placement head and a placement headsupport comprising a placement head alignment device according to afirst embodiment of the invention in the unloaded state;

FIG. 6 shows a side view of the arrangement of FIG. 5 during pressingagainst a substrate;

FIG. 7 shows the arrangement of FIG. 5 in a spatial representation;

FIG. 8 shows the arrangement of FIG. 6 in a spatial representation;

FIG. 9 shows a side view of a second embodiment of the invention in theunloaded state;

FIG. 10 shows a side view of the arrangement of FIG. 9 when pressedagainst a substrate;

FIG. 11 shows the arrangement of FIG. 9 in a spatial representation;

FIG. 12 shows a side view of a third embodiment of the invention in theunloaded state;

FIG. 13 shows the arrangement of FIG. 12 when pressed against asubstrate;

FIG. 14 shows a spatial, partly sectional representation of a fourthembodiment of the invention;

FIG. 15 shows the arrangement of FIG. 14 together with an XYZ handlingsystem;

FIG. 16 shows a side view of a fifth embodiment of the invention in theunloaded state;

FIG. 17 shows the arrangement of FIG. 16 when pressing against asubstrate;

FIG. 18 shows the arrangement of FIG. 16 in a spatial representation,and

FIG. 19 shows the arrangement of FIG. 17 in a spatial representation.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 5 to 8 are used for illustrating a first embodiment of thekinematic holding system in accordance with the invention.

The holding system comprises a placement head support 1 on which aplacement head 2 of a placement apparatus is mounted in an articulatedmanner by means of a joint 4. The placement head 2 carries at the bottomend a component holder 5 with a bottom contact surface 6 in order tohold an electronic or optical component 7 especially by means ofnegative pressure. The component 7 rests in a plane-parallel manner onthe bottom contact surface 6.

Such a placement apparatus is used in the known manner to receive thecomponent 7 in a picking station (not shown), to move it by means of anXYZ handling system to a precisely predetermined location above thesubstrate 3, and to subsequently place the component 7 on the substrate3. The placement head support 1 is part of a placement head guide device18 which is merely shown in FIG. 15 and which comprises severalcarriages that will be described below in closer detail and enables adisplacement and a precise guidance of the placement head 2 in the X, Yand Z direction. The kinematic placement head holding system inaccordance with the invention can also be used together with otherplacement head guide devices or handling systems, especially rθ handlingsystems, in which the position of the placement head is determined bythe distance from a rotational axis and an angular position.

In the illustrated embodiment (FIGS. 5 to 8), the substrate 3 lies inthe XY plane and therefore in a horizontal plane. The longitudinal axis8 of the placement head 2 is arranged vertically in the unloaded stateof the placement head 2, which is shown in FIGS. 5 and 7, and thereforeextends in the Z direction.

The placement head support 1, which is shown in FIGS. 5 to 8, is builtasymmetrically and comprises a guide section 9 which is guided forexample on a Y-carriage 31 (as shown in FIG. 15) and which is merelydisposed on one side of the placement head 2. A horizontal support arm10 extends from the guide section 9 to the opposite side of theplacement head 2, with the joint 4 being arranged at the end of saidsupport arm 10. The joint 4 and the guide section 9 are thereforedisposed on opposite sides of the placement head 2.

A console 11 is fixed to the placement head 2, said console 11surrounding the placement head 2 in the manner of a flange and beingarranged with vertical distance from the support arm 10. The console 11is connected on the one side of the placement head 2 via the joint 4 inan articulated and therefore pivotable manner to the support arm 10. Onthe opposite side of the placement head 2, the console 11 is supportedon the support arm 10 by means of a length-variable holding member inform of a spring 12. The change in length of the spring 12 thereforechanges the angle which the console 11 and therefore the placement head2 assume relative to the placement head support 1.

When the placement head 2 is displaced downwardly and the component 7 ispressed against the substrate 3, a reaction force F which corresponds tothe pressing force is exerted on the placement head 2 and the placementhead support 1, as is shown in FIG. 6. Said reaction force F istransferred from the placement head 2 to the placement head support 1both via the joint 4 and also via the spring 12. If this reaction forceleads to a deformation of the placement head guide device 18 andtherefore to an inclined position of the placement head support 1 (asshown in FIGS. 6 and 8), this deformation is compensated by a change inlength of the spring 12 in such a way that the original alignment of theplacement head 2 (i.e. its vertical alignment) is maintained. For thispurpose the stiffness of the spring 12 is adjusted to the stiffness ofthe entire system in such a way that the change in length of the spring12 corresponds to the deformation-induced displacement of the joint 4 inthe Z direction. Consequently, the console 11 will always be held in thehorizontal position irrespective of any deformation-induced inclinedposition of the placement head support 1. The angular position of theplacement head 2 relative to the substrate 3 is therefore maintainedduring the pressing process, even in the case of a deformation of theplacement head guide device 18.

A second embodiment of the holding system in accordance with theinvention will be explained below by reference to FIGS. 9 to 11.

In this embodiment, the placement head 2 is supported in its upper endregion in an articulated manner by means of a single-axis joint 4 on thesupport arm 10 of the placement head support 1, which support arm isheld on one side. In FIG. 9, the support arm 10 extends again in thehorizontal direction, whereas the longitudinal axis of the placementhead 2 extends in the vertical direction. The placement head 2 ismounted in pendulum fashion on the placement head support 1 via thejoint 4. The relative position of the placement head 2 relative to theplacement head support 1 is set there by way of a length-variableholding member in form of a travel-controlled or force-controlledactuator 13, which rests on the one hand on the placement head support 1and on the other hand on the placement head 2. The drawing shows that inthis embodiment the longitudinal axis 14 of the actuator 13 extendshorizontally and therefore perpendicularly to the longitudinal axis 8 ofthe placement head 2. Furthermore, the longitudinal axis 14 intersectsthe longitudinal axis 8 in a point of intersection S, which is disposedwith substantial distance beneath the joint 4. This allows producingrelatively large torques about the joint 4 with relatively low actuatingforces of the actuator 13. In the case of a respective extension orreduction in length of the actuator 13, the angle of the placement head2 relative to the placement head support 1 changes in such a way thatthe tilt axis error is compensated.

The actuator 13 may especially be an electric direct drive, a voice coilor a piezo drive.

If a deformation of the placement head guide device 18 occurs during thepressing of the placement head 2 against the substrate 3, as isschematically shown in FIG. 10, the actuator 13 will be reduced inlength in the illustrated embodiment in such a way that the verticalalignment of the placement head 2 is maintained. This means in otherwords that the placement head 2 is pivoted relative to the placementhead support 1 about the same angle about which the placement headsupport 1, as a result of the reaction force F, tilts relative to thestarting position.

The respective drive control of the actuator 13 occurs in such a waythat the reaction forces F acting on the holding system or thedeformation paths are measured by suitable sensors and the outputsignals of these sensors are converted by a suitable control device intoactuating signals for the actuator 13.

A third embodiment of the invention will be explained by reference toFIGS. 12 and 13. In this embodiment, the placement head 2 is connectedvia a special rod kinematic system in form of joint rods 15 a, 15 b anda length-variable holding member in form of a length-variable joint rod16. The joint rods 15 a, 15 b, 16 are connected to the placement headsupport 1 on the one hand and to the placement head 2 on the other handin an articulated manner, and arranged in such a way that a specificangular position of the placement head 2 relative to the placement headsupport 1 is maintained at a predetermined length of the joint rod 16.Any change in the length of the joint rod 16 produces a change in theangle of the joint rods 15 a, 15 b and therefore a change in the angleof the placement head 2 relative to the placement head support 1.

The change in length of the two-part joint rod 16 occurs either via apassive holding member in the form of a spring 12 or an active holdingmember in form of a travel-controlled or force-controlled actuator 13,which can be controlled in the same manner as described in connectionwith the second embodiment.

If a deformation or a tilting of the placement head support 1 relativeto the placement head 2 occurs during pressing of the placement head 2or the component 7 against the substrate 3 as a result of the reactionforce F, which deformation produces a respective change in the angle ofthe joint rods 15 a, 15 b, the length of the joint rod 16 is changed insuch a way (reduced in length in the embodiment) that the desiredalignment of the placement head 2 (i.e. the vertical position) relativeto the substrate 3 will be maintained.

A fourth embodiment of the invention will be explained by reference toFIGS. 14 and 15. This embodiment operates similarly to the embodiment asexplained with reference to FIGS. 9 to 11, wherein the placement head 2is not built as a one-dimensional pendulum but as a pendulum that can bepivoted multi-dimensionally. For this purpose, the placement head 2comprises a joint 4′ at its upper end which represents a sphericalbearing. It may especially be an air bearing, a hydrostatic bearing, amechanical spherical head bearing or a ball-bearing spherical headbearing. Furthermore, the joint 4′ can also be arranged as a universaljoint or a multi-axial solid joint.

The position of the placement head 2, i.e. its pivoting positionrelative to the placement head support 1, is determined by two actuators13 which are arranged angularly with respect to each other and which actin a bottom region of the placement head 2 on said placement head. As isshown in the drawings, the two actuators 13 are expediently arranged ata right angle with respect to each other, wherein one actuator 13 actsin the X direction and the other actuator 13 in the Y direction. Byreducing or extending the length of one or both actuators 13, a pivotingmovement of the placement head 2 can be performed in space, by means ofwhich the tilt and therefore the angle of the bottom surface of thecomponent 7 relative to the substrate 3 can be changed and adjusted.

The actuators 13 may again be travel-controlled or force-controlleddrives, which are connected with direct linkage or via a suitablekinematic system (i.e. via levers or a gear) to the placement head 2 onthe one hand and the placement head support 1 on the other hand.

FIG. 14 shows further that the actuators 13 are connected via electricallines to a control unit 17, via which they receive respective movecommands.

The placement process is appropriately performed in such a way that theactuators 13 which cooperate with the placement head 2 are blockedexpediently until contact of the component 7 with the substrate 3, sothat during the rapid displacement of the placement head 2 nouncontrolled pendulum movements of the placement head 2 occur. Theblockage of the actuators 13 is released directly before the touchdownof the placement head 2 or the component 7 on the substrate 3, therebyallowing a free movement of the placement head 2 about the joint 4′.During pressing of the component 7 against the substrate 3, the reactionforce F which corresponds to the pressing force propagates via the joint4′ and the placement head support 1 to the XYZ handling system and leadsto a deformation of the same. The two actuators 13 are controlled viathe control unit 17 in such a way that they change the distance of theplacement head 2 from the placement head support 1 in the X and/or Ydirection in such a way that the predetermined alignment of theplacement head 2 (the vertical alignment in the present case) ismaintained.

The placement head guide device 18, which is schematically shown in FIG.15, can be used in all embodiments of the invention. It comprises Xguides 28, on which a transverse carriage 29 is movable in the Xdirection. The transverse carriage 29 comprises Y guides 30 on which a Ycarriage 31 is movable in the Y direction. Z guides (not shown in closerdetail) are provided on the Y carriage 31, on which the placement headsupport 1 is movable in the Z direction. The X guides 28, the transversecarriage 29, the Y carriage 31 and the Z guides between the Y carriage31 and the placement head support 1 are part of the XYZ handling system.

The placement head compensation apparatus in accordance with theinvention is not limited to the use in such a placement head guidedevice 18. Instead, a combination with random placement head guidedevices is possible.

The alternative possibilities for operating the kinematic holdingsystems in accordance with the invention, in which active holdingmembers such as actuators 13 are used for axis error compensation, canbe described as follows:

-   1. Once the component 7 touches the substrate 3 during the placement    process, the actuator(s) 13 will be switched to be force-free. The    friction between the substrate 3 and the component 7 fixes the    component 7. The occurring deformations will be compensated during    the application of the pressing force.-   2. As soon as the component 7 touches the substrate 3, the    actuator(s) 13 will exert a specific force or variable forces in    order to keep the component 7 at position.-   3. After the component 7 has touched the substrate 3, the    actuator(s) 13 will be displaced along a specific path in order to    keep the component 7 at position.

The angle between the placement head support 1 and the substrate 3 cantherefore be set by means of the actuator/actuators 13. The displacementof an actuator 13 can change the axial position of the placement head 2in relation to the substrate 3 and consequently the angle between theplacement head 2 and the substrate 3 can be kept constant at therequired value despite the change in the angle of the placement headsupport 1. As a result of the two-axial embodiment of actuators 13 asshown in FIGS. 14 and 15, the angle can also be kept constant in space.

A fifth embodiment of the holding system in accordance with theinvention will be explained in closer detail by reference to FIGS. 16 to19. This embodiment is built similar to the first embodiment as shown inFIGS. 5 to 8, but with the difference that the spring 12 and the joint 4are not two separate components, but are combined in the form of a solidjoint 20. As is shown in particular in FIG. 18, the solid joint 20 ispart of a solid joint element 21 which comprises two first solid jointarms 22 and one interposed second solid joint arm 23. The two firstsolid joint arms 22 extend at a distance parallel adjacent to oneanother and are connected to each other at an end by means of atransverse arm 24. The second solid joint arm 23 which is arrangedbetween the two solid joint arms 22 is elastically connected at one endto the transverse arm 24 and freely movable at the other end. The secondsolid joint arm 23 can therefore be pivoted in the manner of a tonguerelative to the first solid joint arms 22. The transverse arm 24 andtherefore the solid joint 20 are disposed relative to the placement head2 on the same side as the free end of the support arm 10 of theplacement head support 1.

In the illustrated embodiment, the second solid joint arm 23 is shapedin the manner of a plate, wherein it comprises a through-opening throughwhich the placement head 2 is guided. Furthermore, the placement head 2is rigidly connected to the second solid joint arm 23. When thecomponent 7 is placed on the substrate 3 and pressed against the same(as shown in particular in FIG. 17), the free end of the second solidjoint arm 23 pivots upwardly relative to the first solid joint arms 22as a result of the pressing reaction force when the placement head 2 ispressed into the oblique position as shown in FIGS. 17 and 19 which iscaused by the deformation of the placement head guide device 18. Theelasticity of the solid joint 20 is adjusted to the deformation of theplacement head guide device 18 in such a way that the predeterminedalignment of the placement head 2 and consequently the plane-parallelalignment of the component 7 relative to the surface of substrate 3 ismaintained.

It will be explained below in closer detail by reference to FIGS. 3 and4 how the lateral offset a (see FIG. 2) can be minimized by specialarrangement of the rotational axis 26 of the placement head 2 relativeto a deformation rotational axis 25 of the placement head guide device18. This will be further explained in FIGS. 3 and 4 by reference to aplacement head alignment device whose principal configurationsubstantially corresponds to the one shown in FIGS. 16 to 19. Theprinciple of arranging the rotational axes in a specific relativeposition with respect to each other for preventing the lateral offset asexplained by reference to FIGS. 3 and 4 can be applied to allembodiments of the invention.

FIG. 3 shows the placement head guide device 18 and the placement head 2in the unloaded state, i.e. when the placement head 2 or the componentthat is sucked up by the placement head 2 has not yet been placed on thesubstrate 3. This unloaded state is also shown in FIG. 4 with thedot-dash lines. The illustration shows that the rotational axis 26 ofthe placement head 2 is situated in the unloaded state at a lower levelby a measure h₁ than the deformation rotational axis 25, which forms thedeformation-induced rotational center of the placement head guide device18 when the placement head 2 is pressed on the substrate 3 and arespective reaction force F acts from below on the placement head 2(FIG. 4).

FIG. 4 shows the deformation-induced twisting of the placement headguide device 18 after pressing against the substrate 3 and the changedrelative position of the placement head 2 relative to the placement headguide device 18 with solid, unbroken lines. In the illustratedembodiment, as a result of the reaction force F, the rotational axis 26of the placement head 2 pivots upwardly in a counterclockwise manner ona circular arc about the deformation rotational axis 25 of the placementhead guide device 18. If the placement head guide device 18 acts in sucha way that the rotational axis 26 of the placement head 2 lies at thepredetermined pressing force with which the components are pressedagainst the substrate 3 by a measure h₂ above the deformation axis 25which is as large as the measure h₁ by which the rotational axis 26 liesin the unloaded state beneath the deformation rotational axis 25, thelateral offset a which occurs by the deformation is equal 0. It istherefore advantageous for minimizing the lateral offset a when therotational axis 26 is situated at a lower level in the unloaded statethan the deformation rotational axis 25, whereas the rotational axis 26is situated at the same level under half the placement force and abovethe deformation rotational axis 25 under full placement force.

FIG. 4 shows that a straight line 1 through the rotational axis 26 ofthe placement head joint and the deformation rotational axis 25 of theplacement head guide device 18 is situated in the unloaded state lowerby an angle −α than a horizontal plane h which is situated at the heightof the deformation axis 25. When the placement head 2 or the componentis pressed against the substrate 3, said straight line, which isdesignated with reference numeral 1′ in FIG. 4, is higher by the angle+α than the horizontal plane h. It is advantageous within the goal ofminimizing the lateral offset a when said straight line 1 moves withinan angular range which lies between +45° and −45° relative to thehorizontal plane h. The scope of the movement is usually relativelysmall and is typically 10° at most, preferably 5° at most. In thisrespect it is also possible as an alternative to the embodiment shown inFIG. 4 that the rotational axis 26 moves between the unloaded and loadedstate in such a way that the straight line 1 either moves only in the“−α” range or only in the “+α” range.

The invention therefore provides a kinematic holding system in which adeformation of the placement head guide device 18 which is caused by thepressing is compensated in at least one axis. This is either realized bya passive element as described above by reference to the first and fifthembodiment, or by means of at least one active element in form of anactuator 13, as explained in connection with the second to fourthembodiments. When passive elements are used, the adjustment of thedeformation of the overall system with the geometric arrangement and thestiffness of the passive element is relevant. The passive tiltcompensation is provided without the actuator 13 and can be integratedboth in the placement head support 1 and in the placement head 2.

It is further possible to arrange the length-variable holding membersfor the placement head 2 or the solid body joint element 21,respectively, or to combine several of the holding members or solidjoint elements 21 with each other in such a way that not onlydeformation-induced pivoting movements of the placement head guidedevice 18 about the Y axis (as shown in the drawings) are compensated,but also pitching and/or rolling movements of the placement head 2 aboutother axes caused by the pressing force.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art having thebenefit of this disclosure that many more modifications than mentionedabove are possible without departing from the inventive concepts herein.The invention, therefore, is not to be restricted except by the appendedclaims and their equivalents.

The invention claimed is:
 1. Kinematic holding system for a placementhead of a placement apparatus for mounting electronic or opticalcomponents on a substrate, comprising: a placement head guide devicecomprising a placement head support for holding the placement head; anda placement head alignment device for adjusting the alignment of theplacement head relative to the placement head support, wherein theplacement head alignment device comprises a joint via which theplacement head is supported in an inclination-adjustable way on theplacement head support, and wherein the placement head alignment devicecomprises at least one length-variable holding member which is arrangedat a distance from the joint between the placement head support and theplacement head and which determines a pivoting position of the placementhead relative to the placement head support and whose length ischangeable during the placement operation depending on a deformation ofthe placement head guide device caused by a pressing force of theplacement head against the substrate in such a way that an axis error ofthe placement head caused by the deformation of the placement head guidedevice is compensated.
 2. Holding system according to claim 1, whereinthe length-variable holding member has a longitudinal axis which isarranged parallel or transversely to a longitudinal axis of theplacement head.
 3. Holding system according to claim 1, wherein theplacement head is pivotably mounted by means of a placement head consoleon the placement head support, and wherein the length-variable holdingmember is supported on the placement head console.
 4. Holding systemaccording to claim 1, wherein the placement head alignment devicecomprises a plurality of joint rods which are connected via joints bothto the placement head and also the placement head support, and whichhold the placement head in a predetermined variable position relative tothe placement head support, wherein the relative position of the jointrods is variable by means of the length-variable holding member in sucha way that a deformation-induced axis error of the placement head iscompensated.
 5. Holding system according to claim 1, wherein thelength-variable holding member consists of a passive element in form ofa spring, which is arranged in such a way between the placement headsupport and the placement head that the pressing force is transferred bythe placement head support to the placement head via the joint on theone hand and via the spring on the other hand, wherein a reaction forceproduced by the pressing force produces a change in a length of thespring.
 6. Holding system according to claim 1, wherein thelength-variable holding member consists of an actuator which is eithertravel-controlled or force-controlled.
 7. Holding system according toclaim 6, wherein the actuator comprises an electric direct drive, avoice coil or a piezo drive.
 8. Holding system according to claim 6,wherein the actuator acts on an axial position of the placement head viaa lever arrangement or a gear.
 9. Holding system according to claim 1,wherein the placement head alignment device comprises a motion blockingdevice for blocking the relative movements of the placement headrelative to the placement head support.
 10. Holding system according toclaim 6, wherein the actuator is formed as a lockable actuator. 11.Holding system according to claim 1, wherein the placement head issuspended in its upper or bottom end region in pendulum fashion on theplacement head support, and is supported in a Z direction by means of ajoint which has at least one rotary degree of freedom, and that the atleast one length-variable holding member is provided beneath or abovethe joint for adjusting the inclination of the placement head relativeto the placement head support.
 12. Holding system according to claim 11,wherein the joint is arranged as a single-axis joint, ball-and-socketjoint or a universal joint.
 13. Holding system according to claim 1,wherein a plurality of length-variable holding members is provided,which are arranged in such a way that they act from different directionson the placement head, so that the placement head can be pivotedmulti-dimensionally in space.